Systems for treating liquids, especially for analysis, are applied, for example, in process measurements technology or in industrial measurements technology. For example, analytical systems can be applied for monitoring and optimizing the cleaning effectiveness of a clarification plant, for monitoring drinking water or for quality monitoring of food. Measured and monitored are, for example, the content of special substances in a liquid sample, for example, the content of ions, such as ammonium, phosphate or nitrate, or biological or biochemical compounds, such as hormones, or microorganisms, e.g. bacteria.